Method for producing a laminated glass pane free of optical obstruction caused by warping, use of a particular carrier film for the production of the laminated glass pane and carrier films particularly suitable for the method or the use

ABSTRACT

The invention relates to a method for producing a laminated glass pane free of optical obstruction, caused by warping, in reflected and transmitted light. The laminated glass pane comprises a first pane of glass, a second pane of glass and a multilayer spacer layer comprising a first composite film, a biaxially-stretched, thermoplastic carrier film provided with a thin layer system, and a second composite film. A carrier film provided with the thin layer system is mounted on the first composite film and has a thickness of from 30 to 70 μm and a degree of heat shringage of from 0.3 to 0.8%, measured after a heat treatment of 20 seconds at 120° C., in both directions. The second composite film is mounted on the carrier film. The packet of films is arranged between the two panes of glass so as to be wrinkle-free, pressed using pressure and heat and made into a composite with the panes of glass. A suitable carrier film and the use thereof for producing the laminated pane of glass are also disclosed.

RELATED APPLICATION

[0001] This application is a continuation of application Ser. No.09/043,366 filed Jul. 31, 1998, which is hereby incorporated byreference. This application is claiming the benefit under 35 U.S.C. §120of said Application.

BACKGROUND OF THE INVENTION

[0002] The invention relates to a process for the manufacture of alaminated safety glass pane which in reflected and transmitted light isfree from wrinkle-related optical distortions, comprising a first glasspane, a second glass pane and a multi-layer intermediate layer, whichintermediate layer in the form of a foil laminate consists of a firstlaminating foil, a bi-axially stretched thermoplastic carrier foilprovided with a thin-film system, and a second laminating foil. Theinvention furthermore relates to the use of a carrier foil for themanufacture of the laminated safety glass pane as well as to a carrierfoil particularly suitable for the process and the use respectively. Thelaminated safety glass panes may be either flat or curved panes. Theflat laminated safety glass panes are used for a great variety ofapplications, e.g. in the building industry or as side windows of motorvehicles. The term curved laminated safety glass panes denotes, withinthe framework of the invention, singly curved and, in particular, doublecurved (spherically bent) laminated safety glass panes, and alsoso-called complex curved laminated safety glass panes, which at least insome parts have large curvatures, i.e. small radii of curvature. Complexcurved laminated safety glass panes are used, in particular, aswindscreens or rear windows of motor vehicles.

SUMMARY OF THE INVENTION

[0003] With the described laminated safety glass panes the thin-filmsystem forms a so-called functional layer. This serves to produce thelaminated safety glass panes in such a way that they can fulfil otherfunctions. These functions include, among others, the heatability, thechanging of the light and energy transmission degree and reflectancerespectively, and the fitting with antennas for the most varying uses.The structure of the thin-film systems and the production thereof areknown and proven. Particularly suitable are thin-film systems based onsilver layers or semi-conductive metal oxide layers. These thin-filmsystems are integrated into the laminated safety glass pane with the aidof a transparent thermoplastic carrier. With regard to the state of theart reference is made in so far, for example, to the WO 90/08334, whichdescribes known carrier foils, proven thin-film systems and alsocustomary laminating foils.

[0004] Laminated safety glass panes of the type described at the outsetoften display optical distortions, in particular in reflected light.These optical distortions are caused by phenomena that can be attributedto corrugations in the carrier foils. The optical distortions occur inflat laminated safety glass panes of the described type as well as incurved, especially complex curved laminated safety glass panes.

[0005] The known measures from which the invention proceeds (EP 0 077672) relate to a selectively light-transmitting or electricallyconductive film on a carrier foil, which has a thickness between 12 and125 μm and after a heat treatment at 120° C. for 30 minutes displays aheat shrinkage which depends in a complicated manner on the thickness ofthe carrier foil. This serves to avoid optical distortions in alaminated safety glass pane, in which the carrier foil is integratedwith the thin-film system. Also here the laminated safety glass pane maybe flat or curved. Tests have shown that the results that can beobtained according to these teaching are open to criticism. The problemsdescribed at the outset, which occur with flat as well as with complexcurved laminated safety glass panes, especially in the case of smallradii of curvature, are not dealt with.

[0006] To prevent that a carrier foil provided with a thin-film system,in particular one of polyethylene terephthalate, which is integrated ina laminated safety glass pane of the type described at the outset,during the manufacture of the laminated safety glass pane changes itsproperties and as a result thereof causes optical distortions, it isknown (EP 0 457 209 A2) to bi-axially stretch the carrier foil attemperatures above the so-called glass temperature, followed bythermo-fixing, and after the thermo-fixing to carry out a furtherstretching at temperatures below the glass temperature. The measuresknown in this respect are complicated, the result is unsatisfactory. Theproblems mentioned at the outset are not dealt with.

[0007] The invention is based on the technical problem to indicatesimple measures suitable for an industrial series production of thelaminated safety glass pane, with which flat as well as curved laminatedsafety glass panes of the type described at the outset can bemanufactured, which do not display optical distortions in reflectedand/or transmitted light.

[0008] To solve this technical problem, the subject of the invention isthe process according to patent claim 1.

[0009] The deaeration which belongs to the teachings of the invention iscustomary and necessary to avoid in the laminated safety glass panedistortions caused by air inclusions. The deaeration must take placeeffectively and adequately in respect of the laminated safety glass paneas a whole as well as in respect of the foil laminate consisting oflaminating foils and carrier foils. The characteristic 1.2) is to beunderstood as meaning that the laminating technology customary in themanufacture of laminated safety glass is used. The process stepaccording to characteristic 1.1) includes the possibility of producing apre-laminate of the first laminating foil and the carrier foil as wellas, optionally, the second laminating foil. The foils that must bepre-laminated are in this case drawn off, in particular, from stockrolls and joined together using pressure and heat with a simultaneous orprior deaeration, before the pre-laminates produced in this manner arecut to size and placed between the two glass panes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0010] In detail, there exists within the framework of the inventionseveral possibilities for carrying out the process according to theinvention. According to a preferred embodiment of the invention apre-laminate of the first laminating foil and the carrier foil is placedon the first glass pane, and then the second laminating foil is put ontothis. This method of operation can be recommended when a secondlaminating foil is used which is not available on rolls, as is knownfrom the use of laminating foils with anti-glare strip that arestretched according to the shape of windscreens. When curved laminatedsafety glass panes must be made, a pre-laminate will be applied on theconcave side of the first glass pane. After applying the pre-laminate apre-pressing can be carried out using pressure and heat and then thesecond laminating foil can be put on and pressed. It lies within theframework of the invention to work with a pre-laminate which comprises afirst laminating foil, the carrier foil provided with the thin-filmsystem and the second laminating foil. However, it is also possible toproceed in such a way that the first laminating foil, the carrier foiland the second laminating foil are put onto the first glass pane andthen the pressing of the complete laminate is carried out. When curvedlaminated safety glass panes must be produced, the first laminating foilwill be applied on the concave side of the first glass pane. Althoughwithin the framework of the measures according to the invention it isrecommended to work as described, when manufacturing curved laminatedsafety glass panes it is also possible to proceed the other way aroundand to apply the laminating foil or the pre-laminate onto the convexside of the first glass pane. Care must always be taken that during thisapplication wrinkles are not already formed in a laminating foil or inthe carrier foil.

[0011] With the process according to the invention distortingdeformations in the carrier foil as well as a destruction of thethin-film system are avoided or suppressed. The invention proceeds fromthe discovery that the described optical distortions in reflected lightcan be attributed to wrinkles with amplitudes in the micrometer range.These wrinkles occur as a result of incorrect handling and when usingunsuitable carrier foils within the framework of the usual laminatingprocesses, also in particular during the required deaeration processesand when using pressure and heat to join the constituents of thelaminated safety glass panes to one another. The risk of the formationof such wrinkles is particularly great when curved, in particularcomplex curved glass panes are made. If in the course of the manufactureof the laminated safety glass pane the carrier foil has wrinkles, thiswill be visible mainly when looking at the reflection.

[0012] Surprisingly, with the process according to the invention opticaldistortions in transmitted and, in particular, reflected light areavoided. The state of the art does not lead one to assume that theinvention would achieve this, and this not only with regard to themanufacture of flat laminated safety glass panes, but also with regardto the manufacture of curved and complex curved laminated safety glasspanes. This also applies when the complex curves are so large thatcuring the adaption of the carrier foil with the thin-film system tothese curvatures, a considerable wrinkling could be expected. Thisapplies, in principle, to all laminating foils that are commonly usedfor the manufacture of laminated safety glass panes and to all customarycarrier foils with thin-film systems. As laminating foils, in particularfoils based on polyvinyl butyral, ethylenevinyl acetate, polyurethaneand polyvinyl chloride can be used, whereas suitable carrier foilsconsists, in particular, of polyesters and their derivatives, inparticular of polyethylene terephthalates. Other materials for thecarrier foil can be cellulose esters or acryl polymers as well aspolycarbonates and polyvinyl fluorides. The materials must be selectedsuch that they form a dimensionally stable substrate for the thin-filmsystem, that they are compatible with the laminating foils and adhere tothese sufficiently. In addition they have to withstand the laminatingprocess without being damaged, be compatible with the thin-film system,transparent and UV-stable.

[0013] The carrier foil can easily be stretched in such a way that theindicated heat shrinkage properties are ensured prior to manufacturingthe laminated safety glass panes. Suitable processes are known. Formaking the carrier foils suitable for the process according to theinvention, the starting foils are stretched bi-axially by 1% and more attemperatures above the so-called glass temperature, subsequent to whichthe stretching is thermo-fixed. It is important to control the processfor the application of the thin-film system in such a way that thecarrier foil at most shrinks slightly, so that a shrinkage behavioraccording to the characteristic 1.12) is also still present after thecoating and before the use within the framework of the process accordingto the invention. If need be, an adequate cooling of the carrier foilduring the coating must be ensured, or the foil must be mechanicallyclamped in. Surprisingly, the stretching of the carrier foil in bothdirections required to ensure the heat shrinkage according tocharacteristic 1.12) does not cause double refraction effects in thecompleted laminated safety glass panes. According to a preferredembodiment of the invention, a carrier foil provided with the thin-filmsystem, the heat shrinkage degree of which according to characteristic1.12) lies in the range of 0.3 to 0.6%, is placed on the laminatingfoil.—The individual glass panes of the laminated safety glass paneaccording to the invention have the usual thicknesses. They may consistof normally cooled or chemically or thermally pre-stressed glass. Alsopartially pre-stressed glass panes can be used.

[0014] The described effects, essential to the invention, are obtainedwith normal thicknesses of the laminating foils. These lie in the rangeof 0.38 mm or a multiple thereof. Preferably, a carrier foil with athickness of 40 to 60 μm, preferably approximately 50 μm, is placed onthe first laminating foil. Depending on the materials used and thetemperatures and pressing times during the pressing, special measuresthat ensure the bonding between the laminating foils and the carrierfoil are not necessary. A particularly thorough bonding in this foillaminate is obtained, however, when a carrier foil provided with thethin-film system, which on both surfaces has a surface energy of atleast 40 mJ/m², is placed on the first laminating foil. To this end thecarrier foil can be subjected on the uncoated side to, for example, acorona or plasma treatment.

[0015] The indicated value parameters are particularly advantageous andlargely optimal when laminating foils of polyvinyl butyral (PVB) orethylenevinyl acetate copolymers (EVA) and with a carrier foil ofpolyethylene terephthalate (PET) are used. The pressing according tocharacteristic 1.2) will normally be carried out at a temperature in therange of 120 to 130° C., at a pressure of up to 13 bar. Attention isdrawn once again to the deaeration which is always required prior toproducing a laminate or pre-laminate. The deaeration can take place withthe usual means such as link rollers, a vacuum bag or vacuum lips.

[0016] According to the invention specially prepared carrier foilsprovided with the thin-film system are used for a special purpose, i.e.for the manufacture of laminated safety glass panes that are free fromwrinkle-related optical distortions, in particular curved and complexcurved laminated safety glass panes. This is possible because of themeasures 1.11), 1.12) which are significant for the invention. This alsoapplies to the described pre-laminates (duplet/triplet). The describedand claimed use can also take place in the form of the pre-laminateswhich consist of a laminating foil and the carrier foil as well as,optionally, the second laminating foil. When curved and, in particular,complex curved laminated safety glass panes are manufactured, the foilsystems, in addition to the influences of pressure and temperature, aresubjected to external forces which ensure the adaptation of theoriginally flat foils of the foil system to the single or doublecurvature of the laminated safety glass panes that are to be produced.When manufacturing curved laminated safety glass panes with a doublecurvature, these forces produce, so to speak, compression phenomena.This applies, in particular, when manufacturing complex curved laminatedsafety glass panes. In addition there are the deformations from internalforces which the foils of the foil systems, so to speak, bring withthem. When manufacturing curved laminated safety glass panes with asingle curve, these forces may cause thrust phenomena, and also herethere are the additional influences of the internal forces. Thesituation is similar when manufacturing flat laminated safety glasspanes. Surprisingly, the teachings of the invention in all cases solvethe technical problem that forms the basis of the invention. This alsoapplies when additional mechanical influences (formation of air flowchannels) occur during the deaeration.

[0017] The invention also covers carrier foils which are particularlysuitable for the described process and the described use, respectively.These carrier foils form the subject of patent claims 15 to 19.

[0018] In the following the invention will be explained in greaterdetail with reference to an exemplified embodiment. The exemplifiedembodiment relates, without limitation, to the manufacture of complexcurved laminated safety glass panes.

[0019] An 0.38 mm thick PVB laminating foil of the firm Monsanto,grained on both sides, a PET carrier foil with a highly light-permeablesun protection film with a double silver layer (product designation XIR75) of the firm Southwall, as well as a second 0.38 mm thick laminatingfoil of the firm Monsanto, grained on both sides, were drawn off fromrolls and joined together at about 60 to 70° C. between a pair ofrollers, to form a deaerated and partially glued pre-laminate, whichnext was cut to the required dimensions.

[0020] Prior to the coating, the PET carrier foil had been bi-axiallystretched and thermo-fixed. The stretching and coating had taken placeunder such conditions that the PET carrier foil, after the coating andprior to the manufacture of the pre-laminate, displayed the folowingheat shrinkage behaviour.—During a 20 second immersion in a liquid bathof polyethylene glycol (molecular weight about 400), heated to 120° C.,the coated PET carrier foil shrunk by about 0.4% in the foil planeparallel and perpendicular to the longitudinal stretching. The measuringtook place by clamping both ends of a foil strip with a length of 150 mmand a width of 15 mm between the jaws of a length measuring device. Thelength of the foil strip is measured prior to the immersion in thetemperature bath and on completion of the heat treatment, at the samestarting temperature. From this the percentage of the change in lengthis calculated as the shrinkage value at a given shrinking temperatureand dwell time.

[0021] The coated PET carrier foil, to ensure an adequate adhering tothe laminating foil, had a surface energy on both sides of more than 40mJ/m².

[0022] The pre-laminate produced as described was placed free fromwrinkles on the concave side of a complex curved glass pane with athickness of 2.1 mm. The glass pane was curved in the longitudinal aswell as in the transverse direction and had sharply curved side parts.Along its edge it was provided with a printed on and burned in opaqueanti-glare strip. Then a second complex curved glass pane, with athickness of 1.5 mm, the curving of which corresponded to that of thefirst glass pane, was placed on the pre-laminate. The edges of thepre-laminate sticking out over the edges of the glass panes were cutoff. Around the edge of the pane, as generally known from themanufacture of curved laminated safety glass, a lip profile was providedconnected to a vacuum system for the purpose of the deaeration.

[0023] During the subsequent deaeration process, a vacuum was applied tothe lip profile for about 20 minutes, and by doing so the glass-foilpack was deaerated. Next, whilst maintaining the vacuum, it waspre-laminated in an autoclave with the aid of a heat treatment of abouthalf an hour at a maximum temperature of approximately 100° C. This wasfollowed, after an interim cooling, by the actual laminating process inan autoclave with a heating of the pre-laminated glass-foil pack toabout 125° C. and a pressure treatment at up to 13 bar.

[0024] After removing it from the autoclave, the reflection andtransmission optics of the completed laminated safety glass werechecked. Also in the area of the more sharply curved side parts of theglass pane, the coated PET carrier foil was practically wrinkle-free andthe glass pane met the stringent requirements on windscreens or rearwindows of motor vehicles in respect of safety properties andreflection/transmission optics.

[0025] Comparison tests with coated carrier foils, the heat shrinkagebehaviour of which was clearly outside the range claimed by theinvention, which therefore during a heat treatment at 120° C. for 20seconds shrunk by less than 0.3%, did not result in laminated safetyglass which was free from optical distortions, which in particularbecame noticeable by a bothersome wash-board effect in the reflectionoptics of the glass panes. When using carrier foils which clearly shrankby more than 0.8%, the so-called orange peel skin effect was observed,which occurs as a result of the formation of irregular elevations anddepressions in the carrier foil. Also tests with carrier foils outsidethe claimed thickness range did not, on the whole, lead to satisfactoryresults.

1. A process for the manufacture of a laminated safety glass pane whichin reflected and/or transmitted light is free from wrinkle-relatedoptical distortions, comprising a first glass pane, a correspondingsecond glass pane and a multi-layer intermediate layer, whichintermediate layer in the form of a foil laminate consists of a firstlaminating foil, a bi-axially stretched thermoplastic carrier foilprovided with a thin-film system, and a second laminating foil, with thecharacteristics: 1.1) Placed on the first laminating foil is a carrierfoil provided with the thin-film system, which 1.11) has a thickness of30 to 70 μm and 1.12) in both stretching directions displays a heatshrinkage degree of 0.3 to 0.8%, measured after a heat treatment of 20seconds at 120° C., and the second laminating foil is placed on thecarrier foil, 1.2) the foils according to characteristic 1.1) arearranged wrinkle-free between the two glass panes and pressed, usingpressure and heat, as well as joined to the glass panes, wherein withinthe framework of the measures according to 1.1) and/or 1.2) at least onedeaeration is carried out.
 2. A process according to claim 1 , whereinon the first glass pane a pre-laminate consisting of the firstlaminating foil and the carrier foil is placed and the second laminatingfoil is placed on the pre-laminate.
 3. A process according to claim 2 ,wherein after applying the pre-laminate, a pre-pressing is carried outusing pressure and heat, and subsequently the second laminating foil isput on and pressed.
 4. A process according to claim 1 , wherein onto thefirst glass pane the first laminating foil, the carrier foil and thesecond laminating foil, a pre-laminate of these foils is applied andsubsequently the pressing is carried out.
 5. A process according toclaim 1 , wherein on the first laminating foil a carrier foil providedwith the thin-film system is placed, the heat shrinkage degree of whichaccording to characteristic 1.12) and 2.12) respectively lies in therange of 0.3 to 0.6%.
 6. A process according to claim 1 , wherein on thefirst laminating foil a carrier foil is placed, which has a thickness of40 to 60 μm, preferably approximately 50 μm.
 7. A process according toclaim 1 , wherein on the first laminating foil a carrier foil providedwith the thin-film system is placed, which on both surfaces has asurface energy of at least 40 mJ/m².
 8. A process according to claim 1 ,wherein laminating foils are used based on polyvinyl butyral orethylenevinyl acetate and a carrier foil of polyethylene terephthalate.9. A process according to claim 1 , wherein the pressing according tocharacteristic 1.1) is carried out at a temperature in the range of 115to 135° C. with a pressure of maximum 13 bar.
 10. Use of a carrier foilof stretched thermoplastic plastic provided with a thin-film system,which carrier foil has a thickness of 30 to 70 μm as well as a bi-axialstretching, for the manufacture of laminated safety glass panes, inparticular for the manufacture of laminated safety glass panes which inreflected and/or transmitted light are free from wrinkle-related opticaldistortions, comprising a first glass pane, a corresponding second glasspane and a multi-layer intermediate layer in the form of a foil laminateconsisting of a first laminating foil, the bi-axially stretched carrierfoil and a second laminating foil, wherein the carrier foil in bothstretching directions displays a heat shrinkage degree of 0.3 to 0.8%,measured after a heat treatment of 20 seconds at 120° C.
 11. Useaccording to claim 10 wherein the heat shrinkage degree of the carrierfoil lies in the range of 0.3 to 0.6%.
 12. Stretched carrier foil ofthermoplastic plastic provided with a thin-film system for carrying outthe process according to claim 1 , which has a thickness of 30 to 70 μmand in both stretching directions a heat shrinkage degree of 0.3 to0.8%, measured after a heat treatment of 20 seconds at 120° C. 13.Stretched carrier foil of thermoplastic plastic provided with athin-film system for the use according to claim 10 , which has athickness of 30 to 70 μm and in both stretching directions a heatshrinkage degree of 0.3 to 0.8%, measured after a heat treatment of 20seconds at 120° C.
 14. Stretched carrier foil according to claim 10 ,which has a thickness of 40 to 60 μm.
 15. Stretched carrier foilaccording to claim 12 , which on both surfaces has a surface energy ofat least 40 mJ/m².
 16. Stretched carrier foil according to claim 12 ,which comprises polyethylene terephthalate.
 17. Stretched carrier foilaccording to claim 14 , which has a thickness of approximately 50 μm.18. Stretched carrier foil of thermoplastic plastic provided with athin-film system adapted for use in a laminated safety glass pane, whichhas a thickness of 30 to 70 μm and in both stretching directions a heatshrinkage degree of 0.3 to 0.8%, measured after a heat treatment of 20seconds at 120° C.